The skin is made up of several layers with the upper composite layer being the epithelial layer. The outermost layer of the skin is the stratum corneum that has well known barrier properties to prevent external molecules and various substances from entering the body and internal substances from exiting the body. The stratum corneum is a complex structure of compacted keratinized cell remnants having a thickness of about 10-30 microns. The stratum corneum forms a hydrophobic membrane to protect the body from invasion by various substances and the outward migration of various compounds.
The natural impermeability of the stratum corneum inhibits the administration of most pharmaceutical agents, vaccines and other substances through the skin. Numerous methods and devices have been proposed to enhance the permeability of the skin and to increase the diffusion of various drugs through the skin. Typically, the delivery of drugs through the skin is enhanced by either increasing the permeability of the skin or increasing the force or energy used to direct the drug or vaccine through the skin.
Several methods of enhancing skin permeability have been proposed and used with varying success. One known method uses an adhesive strip that is repeatedly applied to the skin to strip numerous layers of cells from the stratum corneum. Other methods use a scraper such as a scalpel blade to abrade the skin. These methods are usually painful or uncomfortable and increase the risk of infection by excessively reducing the skin barrier function.
Another method of delivering medicaments including drugs through the skin is by physically forming micropores or cuts through the stratum corneum. This method delivers the medicament to the tissue below the stratum corneum, which can enhance the effectiveness of the medicament delivered. The devices for this use include micron-size needles or blades having a length sufficient to pierce the stratum corneum. Examples of these devices include those shown in U.S. Pat. No. 6,050,988 to Zuck; U.S. Pat. No. 5,879,326 to Godshall et al.; and U.S. Pat. No. 5,250,023 to Lee et al.; EP 0 381 410 and WO 97/48440.
The epidermis is a particularly desirable target for vaccine delivery as it is rich in antigen presenting cells. The dermis, in comparison, contains fewer antigen presenting cells (APC's). In addition, the epidermis and the stratum corneum do not contain nerves or blood vessels so this site has the advantage of being essentially painless and blood-free while giving access to the skin layers capable of responding to the antigen.
Techniques and devices for forming furrows in the stratum corneum exist which increase the surface area of the exposed epidermal layer and enhance absorption of a medicament including drugs and pharmaceutical agents or medicament into the body, also are known (EP 1 086 719). However, the technique therein involves lateral movement of the abrader device, which can introduce inconsistencies that vary with the technician, user or patient. The inconsistencies can include the dosage amount of the drug or vaccine and depth of the delivery site. In the past, devices have been proposed which aid in the proper perforation of the skin as in U.S. Pat No. 5,843,114 to Jang (herein referred to as '114). The '114 patent relates to disk perforator system including a switched light emitting diode to indicate proper pressure in a digital fashion.
Thus, there remains a need for a device that is consistent in both delivery of the vaccine, drug solution or other agent and the amount of abrasion to the patient's skin. Accordingly, a continuing need exists in the industry for an improved device for the epidermal administration of various drugs and other substances.